Comparison of the chromatographic behavior of levofloxacin, ciprofloxacin and moxifloxacin on various HPLC phases.

A simple and rapid HPLC method with UV detection was developed for the separation of ciprofloxacin, levofloxacin and moxifloxacin. Chromatography was carried out using a BDS Hypersil C18 (100 x 4.6 mm, 2.4 microm) HPLC column and an isocratic mobile phase consisting of MeOH/25 mM phosphate buffer 28/72 (v/v) at pH 3 and flow rate 1 ml.min-1 . The effect of mobile phase variables such as methanol content, pH and buffer concentration on the chromatographic behavior of the three fluoroquinolones was investigated. The retention behavior on a sub 3 microm C18 column was also compared with that on three different calixarene-bonded and on monolithic stationary phases. The results indicate that some differences exist between these three types of stationary phases, particularly in the effect of buffer concentration on the retention mechanism of the three used FQs on calixarene-bonded stationary phases.

The role of silver nitrate as additive in non-aqueous capillary electrophoresis.

In this study, effect of use of silver nitrate as additive on non-aqueous capillary electrophoresis (NACE) separations of some structurally related compounds belonging to antidepressants, neuroleptics or sulfonamides, was examined. The presence of silver nitrate was found to enhance these NACE separations. The use of silver nitrate provided a successful method of improving the separations of antidepressants, neuroleptics and sulfonamides. The use of cyanomethyl-calix[4]arene (CMCX[4]) in the presence of silver nitrate for the separation of sulfonamides has significantly affected the separation.

Considerations of the behaviour of C18-chains and calixarenes and their application for determination of stationary phase volume in RP-chromatography.

The volume of stationary phase is extremely important for the estimation of thermodynamic information such as entropy and Gibbs free energy in HPLC. However, the definition of this volume strongly depends on the conditions chosen. In the present mini review the partitioning model of small molecules at low concentrations and methanol as modifier is assumed. All the other conditions that could influence the volume of the stationary phase like the thickness of the phase, the area of the phase, the order of C18-chains, the density of the chains, the temperature etc. had to be considered and are therefore reviewed in the present work. The results of the theoretical considerations and a new method of surface estimation were used to calculate the stationary phase volume.

The effect of achiral calixarenes on chiral separation of propranolol-HCl and brompheniramine maleate in capillary electrophoresis using cyclodextrin as chiral selector.

In this study we have examined the effect of achiral water soluble p-sulfonatocalixarenes (SCX[n]) on chiral separation propranolol-HCl and brompheniramine maleate. Several cyclodextrins (CDs) and cyclodextrin derivatives were examined as chiral selectors applying complete filling technique (CFT) accompanied with the partial filling technique PFT of (SCX[n]) as achiral modifier. Only with hydroxypropyl-beta-cyclodextrin (HP-beta-CD) chiral separation could be achieved. The effect of the organic modifier on these chiral separations was examined. The results indicate that at pH 4.65, the use of HP-beta-CD (CFT) alone could not initiate chiral separations of both analytes and these chiral separations could be induced using HP-beta-CD (CFT) followed by SCX[n]/HP-beta-CD (PFT).

Determination of pesticide residues in Khat leaves by Solid-phase extraction and High-Performance Liquid Chromatography

The purpose of this investigation is to develop a simple method for the assessment of pesticides in Khat leaves; Catha edulis FORSK. (Celastraceae) shrub; chewed by about 60of the Yemeni people; producing amphetamine-like psychostimulation. The first procedures involve solid-phase extraction using Adsorbexr RP-C18 and Bakerbondr RP-C18 disposable cartridges with 40acetonitrile for elution. Isocratic and gradient analysis was carried out by means of high-performance liquid chromatography using different stationary phases to analyse methidathion; peconazole and dimethoate. An UltrasphererODS RP-18-column with UV-detection at 210 nm and 80/20(v/v) acetonitrile/water as mobile phase (isocratic) was used to determine the content of methidathion; peconazole and dimethoate (detection limit 20-25 ng). The method was validated with fortified samples at pesticide concentration of 0.1 mg/ml. Average recoveries ranging from 97.9 and 101.6with a relative standard deviation(RSD) of 1.7-3.8. Each recovery analysis was repeated four times. Limits of detection ranged from the analytical procedures were applied to 5 samples of khat and no detectable amounts of pesticides were found in any sample under the conditions described

Capillary electrophoretic separation of enantiomers of amino acids and amino acid derivatives using crown ether and cyclodextrin.

The capillary zone electrophoresis using (+)-18-crown-6-tetracarbonic acid as a chiral selector was a suitable method for the enantiomeric separation of racemates of amino acids and of some amino acid derivatives (esters, dipeptides). The influence of the chemical structure of the compounds on the separation was investigated. After optimization of the separation conditions, baseline separations were obtained for most racemates. The addition of acetonitrile and TBAB yielded an improvement of the separation. Improved selectivity was further observed by the application of a cyclodextrin, HP-beta-CD, in combination with the crown ether.

The effect of the process variables on the HPLC separation of tricyclic neuroleptics on a calixarene-bonded stationary phase.

The chromatographic behavior of a new HPLC-stationary phase with supramolecular selectors on the basis of calixarenes is described for the separation of nine tricyclic neuroleptics. The effects of different chromatographic conditions (buffer system, pH-value, type and content of organic modifier, injection volume) on the separation of the analytes were studied. Additionally, the effect of structural differences of the neuroleptic analytes was studied. The chemical structure and pKa of the neuroleptics highly influenced their separation on the calix[8]arene phase. The separation of all analytes on the investigated calixarene-bonded stationary phase was possible with a mobile phase of acetonitrile with 30 mM ammonium acetate buffer (pH 3.5) 30:70(v/v) using 1 ml/min flow rate.

Chiral separation of amino acid esters by micellar electrokinetic chromatography.

Micellar electrokinetic chromatography (MEKC) was used for the chiral separation of uncharged analytes (C- and N-protected amino acids). Sodium dodecyl sulfate (SDS) was the micelle forming agent, and different cyclodextrin (CD) derivatives were added as chiral selectors. Suitable conditions for the enantioseparation were found by variation of the separation conditions. The influence of addition of organic solvents like acetonitrile or methanol, and other chiral additives (camphor-10-sulfonic acid, malic acid) was examined. The addition of an organic modifier resulted in different effects on micelle formation, and thereby on the separation. The used chiral additives did not improve the selectivity. Furthermore, dependence of the electroosmotic flow (EOF), and the capacity factors on the concentration of CDs was investigated. Increasing the CD concentration, both the EOF to a smaller extent as well as the capacity factors decrease. Nevertheless, the enantioseparation is improved with a CD-concentration up to 30 mM. Higher CD-concentrations reduce the separation of the analytes.

Chiral separations of 1,3,4-thia- and 1,3,4-selenadiazine derivatives by use of non-aqueous capillary electrophoresis.

Our aim was to establish suitable conditions for the chiral separation of 12 1,3,4-thia- and 1,3,4-selenadiazine derivatives; some of them were identified in screening tests as potential antituberculotics. To overcome possible problems with the water insolubility of most analytes, we profited by the advantages of non-aqueous capillary electrophoresis. Methanol, formamide, and a mixture of formamide with acetonitrile (1:2, v/v) were used as separation media. Hydroxyethyl-, hydroxypropyl-, and methyl-beta-cyclodextrin were applied as chiral selectors in concentrations of 200 mM. Besides the effect of these different electrophoretic media and selectors, we also investigated the consequences of using different electrolytes (25 mM ammonium acetate/1 M acetic acid and 25 mM citric acid/12.5 mM TRIS). Distinct differences of the separation factors in the different separation media were observed. Depending on structure characteristics of the analytes, we established clear classifications to these cyclodextrins (CD), which were most appropriate for the separation of the enantiomers of the particular analytes.

Chiral separation of unmodified amino acids with non-aqueous capillary electrophoresis based on the ligand-exchange principle.

A ligand exchange mechanism in non-aqueous capillary electrophoresis was employed for the separation of eight unmodified amino acids using chiral complexes of copper(II) with L-proline and L-isoleucine. The electrophoretic medium consisted of 25 mM ammonium acetate and 1 M acetic acid in methanol. We were able to completely separate the enantiomeric pairs of each of the investigated racemic amino acids. We also report the optimization of the separation parameters, such as pH*, composition of the complex, and concentration of the complexing agents.

New calixarene-bonded stationary phases in high-performance liquid chromatography: comparative studies on the retention behavior and on influences of the eluent.

The chromatographic behavior of six calixarene-bonded stationary phases is reported. Varying analyte selectivities (i.e., for phenols, substituted aromatics, polycyclic aromatic hydrocarbons, barbituric acid derivatives, xanthines) exist as a function of the ring-size of the calix[n]arenes (n=4, 6, 8) and the substitution at the "upper rim" with para-tert.-butyl groups. Although eluents with unusually high proportions of water were used, a comparison with conventional reversed-phase (RP) columns shows a predominantly reversed-phase character with remarkable selectivities of these phases. The influences of several organic solvents on retention variations of solutes are compared for RP-C18, phenyl and calixarene phases.

Nonaqueous capillary electrophoresis: application possibilities and suitability of various solvents for the separation of basic analytes.

Eleven organic solvents were tested for their suitability in the use of capillary electrophoresis (CE). In all cases, 25 mM ammonium acetate and 1 M acetic acid were used as electrolytes. Three basic therapeutical agents, propranolol, carteolol and imipramine, were used as analytes. Four solvents (2-propanol, ethylene glycol, propylene glycol, dichloromethane) were not suitable for use with CE under our conditions. Depending on the other solvents used, the analytes showed very different behavior. We observed that the epsilon/eta quotient alone is not sufficient for a characterization of the solvents. Further investigations with all the solvents as 1:1 mixtures with methanol were carried out. As a result some principal changes occurred compared to the pure solvents. Working with mixtures of different solvents proved to be advantageous because of the possibility to influence properties like high viscosity or low ionizing abilities by the addition of a suitable second solvent.

Effects of quinazoline (3H, 1H)-4-one-2-thiones with axial and central chirality on the contractile response of smooth muscle.

Quinazolines are versatile nitrogen heterocyclic compounds displaying a broad spectrum of biological and pharmacological activities. The influence of some new synthesized quinazolines with axial and central chirality was studied on the isometric muscle tension of rat ileum, rat uterus, and porcine coronary artery. While structural changes of the compounds showed only little influence on peristaltic movement of the ileum, quinazoline derivatives induced a relaxation in the uterus and in the coronary artery depending on the kind and position of the substituent. The introduction of axial chirality into the molecule of modification of the side chain caused an increase in the pharmacological action. These effects could not be inhibited by sympatholytics. So far the mechanisms and receptors causing the spasmolysis are unknown.

[Anti-arrhythmia action of amidinohydrazone substituted benzophenones. 6. Parenteral drug forms of (Z)-2-amino-5-chlorobenzophenone amidinohydrazone acetate (G 256)]. / Antiarrhythmisch wirksame Amidinohydrazone substituierter Benzophenone. 6. Mitteilung: Parenterale Arzneiformen für des (Z)-2-Amino-5- chlorbenzophenonamidino-hydrazonacetat (G 256).

The combination of lyophilized G 256 and a solvent ampoule is recommended as an optimal variant for the application of the compound. In the lyophilized substance both the hydrolysis and the isomerisation are reduced so it is stable enough for the required period of usability.

[The HPLC analysis of chiral beta-receptor blockers]. / Zur HPLC-Analytik chiraler beta-Rezeptorenblocker.

Investigations on direct separation by RP-HPLC of selected enantiomeric beta-adrenergic active agents are described. R- and S-1-phenylethylisocyanate (PEIC) as well as (1S)-(+)-campher-10-sulfonylchloride (CSC) are used for the derivatization of the compounds. Correlations between chromatographic data and various influences (pH, temperature, reaction time, concentration of reagens a.o.) have been discussed. The behaviour of derivatized and underivatized analytes on RP-columns is described in dependence on buffer concentration of the mobile phase. The investigated beta-adrenergic agents were partly separated after derivatization with PEIC, whereas this was not possible with CSC as derivatization reagent.

[Antiarrhythmia active amidinohydrazone substituted benzophenones. 5. The stability of (Z)-2-amino-5-chlorobenzophenone amidinohydrazone acetate in solution]. / Antiarrhythmisch wirksame Amidinohydrazone substituierter Benzophenone. 5. Mitteilung: Untersuchungen zur Stabilität des (Z)-2-Amino-5- chlorbenzophenonamidinohydrazonacetats in Lösung.

The aqueous solution of the title compound can be used for injection for one year if it is stored at room temperature and under light protection. Under these conditions 8% of the E-isomer are produced. The reaction is reversible at day light. Red coloured products of decomposition are formed by long lasting influence of light. At higher temperatures or at sterilisation several products of decomposition are formed which structure is elucidated. For these decomposition a scheme is proposed.

Alterations of purine metabolism in mononuclear cell populations of first degree relatives of insulin-dependent diabetic individuals with disturbed glucose tolerance.

In a T lymphocyte and macrophage-depleted mononuclear cell population of the peripheral venous blood of 10 of 41 first degree relatives of insulin-dependent diabetic individuals who had or had had disturbed glucose tolerance adenine uptake rates were significantly increased, the relative adenine incorporation rates into the adenine nucleotides, however, were diminished. Values were compared with those of 30 controls. In 7 of 9 investigated individuals with increased adenine uptake rates antibody-dependent cellular cytotoxicity against rat Langerhans islets (ADCC) was increased in the same cell population. In these individuals the number of diabetes manifestations was relatively high. Adenine uptake rates, ADCC and glucose tolerance changed with time.